In many actuating devices or actuators, it is necessary or desirable to provide a large transmission ratio between a drive mechanism and/or power source, such as for example, an electric motor and a driven component, such as for example, a release bearing or the like.
It is already known from prior art that several gear stages are to be provided in order to create large transmission ratios. This is possible, for example, by interconnecting several wheel sets in series—relative to the torque flow. An example for this is that a first shaft drives—over a first gear stage—a second shaft, which in turn drives—over a second gear stage—a third shaft, which in turn then drives—over a third gear stage—a fourth shaft if necessary etc. Depending on the targeted overall transmission ratio, a targeted large transmission ratio can be achieved using the number of the shafts and gear stages designed according to this principle and also using the individual transmission ratios of each of the wheel sets interconnected in series.
Furthermore, it is known from prior art that several planetary gears can be interconnected with a view to achieving a large total transmission ratio.
The aforementioned designs thus use several individual transmission ratio stages for creating the large overall transmission ratio.
In addition, designs are also known from prior art in which a large overall transmission ratio can be achieved by means of a single transmission ratio stage.
Devices and/or gears of this type are known, for example, as harmonic gears and/or harmonic speed changers or as cycloid gears.
Examples of harmonic gears are disclosed in U.S. Pat. Nos. 4,619,156 or 4,840,090 and corresponding German Patent No. DE 38 01 387 A1. Examples of cycloid gears are disclosed in U.S. Pat. No. 4,297,920 and corresponding German Patent No. DE 28 30 909 and also in U.S. Pat. No. 4,594,915 and corresponding German Patent No. DE 32 06 992.
The hitherto known harmonic gears and/or harmonic speed changers substantially comprise three parts, namely a wave generator, a flexible gear shaft and/or a hollow flexible part and also a gear ring.
The flexible gear shaft usually comprises a rigid shaft and/or collar, which is connected to a cup-like, thin-walled steel part, which supports on its external casing a circumferentially arranged gear tooth system embodied mostly as a spline. The wave generator is thereby usually a device, which comprises a bearing and also a wave generator plug. The external surface of this wave generator plug usually has an ellipsoidal shape. A specially designed ball-bearing is arranged therearound, which is usually tight-fitted in such a way that it essentially assumes the same ellipsoidal shape as that of the wave generator plug. The wave generator is thereby mostly used as the input part and is usually connected to a servomotor.
For the purpose of installation, the wave generator is inserted into the flexible shaft in such a way that its ball-bearing essentially assumes the same axial position as the gear tooth system of the flexible shaft. The thin wall of the flexible shaft and/or its thin radial external wall of its cup-like contour essentially assume—in the region of one edge—the same ellipsoidal shape of the bearing. Due to this the teeth of the external surface of the flexible shaft are also arranged corresponding to this ellipsoidal shape, so that the flexible shaft has an ellipsoidal pitch circle diameter on its external surface. The flexible shaft is usually used as an output part of the harmonic gear. When in operation, the flexible shaft gets deformed, wherein said deformation is not a sign of wear.
The gear ring is usually a rigid ring with a gear tooth system on its inside. The gear ring is usually fixed in a housing so that it cannot rotate. The gear ring is positioned in such a way that its teeth engage in those of the flexible shaft. The engagement thereby takes place in the region of and/or along the long principle axis of the ellipsoidal shape, so that the ellipsoidally arranged gear tooth system is located essentially concentric to the circular gear tooth system of the gear ring and the ellipsoidal gear tooth system engages with the gear ring tooth system in two opposite regions.
The flexible shaft thereby has two teeth less than the gear tooth system of the gear ring. The transmission ratio is thereby determined by the ratio of the number of teeth of the flexible shaft to the difference in the number of teeth of the flexible shaft and the number of the teeth of the gear ring. Thus, if, for example, the gear tooth system of the flexible shaft comprises 200 teeth and the gear tooth system of the gear ring has 202 teeth, the transmission ratio results of 200/(200−202)=−100, wherein the negative sign indicates that the input side and the output side rotate opposite to one another.
Cycloid gears usually comprise a fast rotating input shaft having an eccentrically arranged radial cam and also a rolling bearing device. Furthermore, they usually comprise a cycloid disk and a slowly rotating output shaft.
Both the hitherto known cycloid gears as well as the harmonic gears and/or harmonic speed changers of the type known so far are designed according to the so-called “on-axis” principle. Thus especially the drive and/or the driving side and the output and/or the output side are arranged on and/or relative to the same axis, thus concentrically, in particular. In order to achieve an “off-axis drive” and/or “off-axis control” in these designs of the known type, one or more transmission ratio stages in addition to the cycloid gear and/or harmonic gear are added, wherein said transmission ratio stages cannot be assigned to the actual cycloid gear and/or the harmonic gear.
The requirement of an “off-axis design” in such embodiments usually leads to the motor or a corresponding drive device being arranged at a distance and is connected using a corresponding connection to the driving and/or driven element, such as for example, a hydraulic connection in hydrostatic systems or a rope and/or belt or a lever or other elements in mechanical systems.